This invention relates, in general, to III-V compound semiconductor or field effect transistors, and more particularly, to a III-V compound semiconductor vertical MESFET (Metal Semiconductor Field Effect Transistor).
Silicon power field effect transistors are well known and are capable of handling up to a thousand volts and several amperes. However, the performance of the silicon devices is ultimately limited by the basic properties of the silicon from which these devices are made. It has been shown in the literature that the on-resistance of power field effect transistors is inversely proportional to the carrier mobility and inversely proportional to the cube of the energy band gap. Using this knowledge it has been predicted that the on-resistance of GaAs FETs is at least twelve times lower than that of silicon FETs of equal semiconductor area and breakdown voltage. However, most of the GaAs FETs found in prior patents are actually MISFETs. An example of such a device is disclosed in U.S. Pat. No. 4,568,958 which issued Feb. 4, 1986 to Baliga. A vertical GaAs MESFET is disclosed in U.S. Pat. No. 4,587,540 which issued May 6, 1986 to Jackson. This MESFET has a top side drain on a mesa with gates on either side of the drain and the source located on the bottom.
It is an object of the present invention to provide a vertical III-V compound semiconductor MESFET having topside source and gate electrodes.
Another object of the present invention is to provide a vertical III-V compound semiconductor MESFET having a low die size yet providing lower device on-resistance, much higher operating frequencies, and higher switching speeds.
A further object of the present invention is to provide a vertical MESFET having a larger bandgap which allows higher doping thereby resulting in lower onresistance.